Abstract

Survival and reproduction of the spotted alfalfa aphid, Therioaphis maculata (Buckton), were similar to those of the pea aphid, Macrosiphum pisi (Harris), at all combinations of three temperatures and three humidities in studies using three alfalfa clones differing in resistance to both aphids. Differences among clones and among temperatures in regard to survival of adults and number of live nymphs produced per adult day were significant for both pea aphids and spotted alfalfa aphids. However, the interaction of clones ✕ temperatures was also highly significant. Differences in resistance among clones were striking at 85º but nil at 55ºF. Humidity had less influence than temperature on aphid biology. Differences in survival of adults and number of live nymphs produced per adult day at 25%, 50%, and 90% relative humidity, expressed as averages of all clones and temperatures, were insignificant. The interaction of clones ✕ humidities was also insignificant which indicated that survival and reproduction of aphids on the clones were about the same irrespective of humidity. However, the effect of temperature was conditioned by humidity. At 85ºF. survival of adults and number of live nymphs produced per adult day differed significantly with humidity, but the differences were insignificant at 55º. Resistance was more apparent when expressed by number of live nymphs produced per adult day than by survival of adults.

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